Runaway Diesel

[a64pilot]

Originally Posted by Jim Cate

In all these scary stories, I'm surprised that valve float didn't limit the revs somewhat. Engines designed to run at slow speeds usually have pretty weak valve springs. Or maybe the float wasn't severe enough to limit unloaded RPM, I dunno... just thinking back to my drag racing engines from years ago, but those engines were surely not "unloaded"!



Jim

They are limited by valve float, and often the demise is when they swallow a valve too. Only one I have seen runaway personally just seized, no exploding anything, looked cool cause there was 2ft of clear exhaust from the pipe before the fire started there was so much fuel being pumped.
I was going to a tech school and the school had gotten a few free Diesels from the marine base, they had been preserved. I de-preserved one, the shop teacher the other, his method of purging oil from the injection system was to put high pressure shop air to the injection pump and blow the air out.
Engine was started with no coolant and immediately ran away, we all stood back a couple of hundred feet and watched, it took a long time to seize, at least a couple of minutes.

From your drag racing days you know actual physical engines blowing up is rare, yes blowers get blown off, sometimes rather spectacularly and clutches do explode, but engines usually at worst bust an oil pan.

[rbk]

Diesels need two things to run, fuel and air. Fuel can be the crank oil. Only reliable/safe option IMOis to smoother with a CO2 extinguisher. This does the least damage you may be able to fix and reausitate after the fact. Mount on a bulkhead where convenient and plumb a hose directly over the intake. No body parts to sacrifice, not panels to remove and almost anyone can install for a minimal price.

[N1EYO]

Originally Posted by Pauls

Some of the old GM diesels had a spring loaded plate which would snap over the intake and choke the engine. All that was required was to pull a lever to actuate the plate. Positive, fast, and simple.

My 8v71 did

[Whitebread117]

Old Post revived, but I'll play.

My 8v71s do - spring loaded air cutoff flappers, triggered remotely from the helm via mechanical linkages.

9.3l (each) is nothing you want to lose control of.

Normal control is electric solenoids on the fuel lines, but the air flappers are peace of mind.

[puffcard]

Had a little Volvo MD 7 one cylinder, run away over 45 years ago. Started, with a failed governor. Lucky that motor had a decompression lever for hand starting, which I pulled. I was only 13, and it was one of the scariest moments of my early days on the water. That shut it down very quickly. Back then, I knew it needed fuel, air and compression. It was the family's first boat and only a year old. In the short time during the runaway, the huge over 150lb flywheel cracked and was very close to coming apart and going thru the hull of the boat. The motor was replaced by Volvo and never had any other problems.

[gjordan]

Turning off fuel in a runaway is usually not going to work since they are running on crankcase oil that had been overfilled and thinned by a leak in the lift pump. When my Perkins ran away the noise and smoke were horrendous . I first tried the kill switch with no result and then dove below and turned the fuel supply off and it kept running. being close to shore I went back up on deck and tacked away from the rocks and the engine immediately dropped to a normal smooth idle. The stop switch shut it down just like normal. The reason it stopped running away was that on the other tack the crank shaft wasnt throwing oil up onto the cylinder walls The smoke was so bad that a dinghy came roaring up to us with a big fire extinguisher. He was sure we were on fire. Put on a rebuilt fuel pump and it only lasted a few hours and I then blocked off the pump mount and put an electric fuel pump. I also kept the air cleaner on with just enough tightness to not vibrate off, but able to twist it off quickly. I kept a piece of plywood near to shut off the air. Trying rags will almost certainly cause bent valves (expensive) and I was later told that CO2 is so cold that it can cause valve damage. years later I was working on a large motoryacht with twin Gardner diesels. At the entrance to the engine room was a big lever that would start the CO2 fire extinguishers, turn off the fuel and shut butterfly valves in the engine air intake. We never had to use it. The GM diesels are different from most small yacht diesels, in that their injectors (and all of the lines) are under the valve cover and a leak on a line could feed enough fuel into the system to cause a runaway. Possibly shutting off fuel could stop a runaway, but if enough fuel had drained down into the sump it might not stop from fuel shutoff. It is always a real scary situation. ____Grant.

[gjordan]

I must add that my Perkins ran fine for years after the runaway. I dont think the RPM actually got very high, it was just the noise (sounded like a sledge hammer inside of an oil drum) and smoke that made it so scary.____Grant.

[Jim Cate]

Originally Posted by a64pilot

They are limited by valve float, and often the demise is when they swallow a valve too.

.....

From your drag racing days you know actual physical engines blowing up is rare, yes blowers get blown off, sometimes rather spectacularly and clutches do explode, but engines usually at worst bust an oil pan.

Yep, that makes sense to me (valve float leading to destruction). The typically small clearance between valve and piston comes into play...

But as to destroying dragster engines, well I did my share. This was long ago (late 50s through late 60s) and really stout aftermarket bits were both rare and out of my budget. I broke a few, all small block Chevy engines, and one in particular stays in the memory bank. When I got it apart, the only re-usable parts were the fuel injection pump (mounted on the front cover and driven by the camshaft) and a few f the roller cam followers. Everything else was scrap:block, crank, all rods and pistons, cam, oil pump, magneto, pan. Oh... a few of the rocker arms were ok and the valve covers too. I remember when I hoisted the remains out of the car, the engine tilted a bit. It sounded like a garbage can full of gravel as all the debris slid about inside. Not a happy day...

Jim

[Snowpetrel]

Originally Posted by a64pilot

About the only way an engine will run on its own oil is of its way overfilled, then the crankshaft will beat the oil into a foam, the foam will fill up the engine and come out of the blowby tube, that is of course plumbed into the suck side of the engine.
Another way is to have fuel leaking into the oil, this will raise the level until eventually it’s high enough to come out the blowby tube.

Almost always an engine with enough blowby to blow enough oil out of the tube to make it run away, has such a low compression that you can’t get it to start, and if you do it fills the area with blue smoke, meaning of course your unlikely to be running the thing to begin with.

Now if it were me, and especially if I were running a turbo, I would not plumb the blowby tube into the suck side of the engine, that is in my opinion pretty stupid, I’d instead run it into a catch can, reasoning is I don’t want to be feeding oil mist into my turbo and intercooler, nastying the things up. But if a blow by tube is not plumbed into the suck side, the engine can’t usually run away from oil.
I say usually as in my younger days I flipped a farm tractor over on myself, and it tried to run away as it was upside down and enough oil was getting past the pistons to run, but it ran poorly and eventually quit after I turned the fuel off.

Had an old engine runaway due to oil on a yacht when I was a kid. Very scary as it reached 4000 rpm or so and nearly shook the whole boat to pieces.

We had burst an oil line and the owner way overfilled the oil after repairing the hose (it started coming out the dipstick...) The old engine was hard to start at the best of times (hooked on aerostart) but this time once she started she rapidly took off and then started spewing partly burnt oil out the exhaust. Of course we shut off the fuel, but their was so much oil in the sump it ran for 10 minutes or so before either chocking itself on partly burnt oil or running out of oil in the sump.

Fortunately we where tied up alongside, so we all got off the boat in fear of the thing exploding. None of us had the knowledge or bravery to get back aboard and block the air intake. The mast was pumping so badly we thought it was going to come down, and the small harbour was filled with vile black smoke and oil.

I am not sure how the crankcase breather was run, prehaps it burnt the overflow or maybe it got past the worn rings?

The engine ran as well (or as badly) as it ever had after this incident.

I mate of mine had a detriot run away on him after someone closed the fuel return without him knowing.